Merge branch 'cc/replace'

* cc/replace:
  t6050: check pushing something based on a replaced commit
  Documentation: add documentation for "git replace"
  Add git-replace to .gitignore
  builtin-replace: use "usage_msg_opt" to give better error messages
  parse-options: add new function "usage_msg_opt"
  builtin-replace: teach "git replace" to actually replace
  Add new "git replace" command
  environment: add global variable to disable replacement
  mktag: call "check_sha1_signature" with the replacement sha1
  replace_object: add a test case
  object: call "check_sha1_signature" with the replacement sha1
  sha1_file: add a "read_sha1_file_repl" function
  replace_object: add mechanism to replace objects found in "refs/replace/"
  refs: add a "for_each_replace_ref" function

.gitignore

@@ -105,6 +105,7 @@ git-reflog
 git-relink
 git-remote
 git-repack
+git-replace
 git-repo-config
 git-request-pull
 git-rerere

Documentation/git-replace.txt

@@ -0,0 +1,71 @@
+git-replace(1)
+==============
+
+NAME
+----
+git-replace - Create, list, delete refs to replace objects
+
+SYNOPSIS
+--------
+[verse]
+'git replace' [-f] <object> <replacement>
+'git replace' -d <object>...
+'git replace' -l [<pattern>]
+
+DESCRIPTION
+-----------
+Adds a 'replace' reference in `.git/refs/replace/`
+
+The name of the 'replace' reference is the SHA1 of the object that is
+replaced. The content of the replace reference is the SHA1 of the
+replacement object.
+
+Unless `-f` is given, the replace reference must not yet exist in
+`.git/refs/replace/` directory.
+
+OPTIONS
+-------
+-f::
+	If an existing replace ref for the same object exists, it will
+	be overwritten (instead of failing).
+
+-d::
+	Delete existing replace refs for the given objects.
+
+-l <pattern>::
+	List replace refs for objects that match the given pattern (or
+	all if no pattern is given).
+	Typing "git replace" without arguments, also lists all replace
+	refs.
+
+BUGS
+----
+Comparing blobs or trees that have been replaced with those that
+replace them will not work properly. And using 'git reset --hard' to
+go back to a replaced commit will move the branch to the replacement
+commit instead of the replaced commit.
+
+There may be other problems when using 'git rev-list' related to
+pending objects. And of course things may break if an object of one
+type is replaced by an object of another type (for example a blob
+replaced by a commit).
+
+SEE ALSO
+--------
+linkgit:git-tag[1]
+linkgit:git-branch[1]
+
+Author
+------
+Written by Christian Couder <chriscool@tuxfamily.org> and Junio C
+Hamano <gitster@pobox.com>, based on 'git tag' by Kristian Hogsberg
+<krh@redhat.com> and Carlos Rica <jasampler@gmail.com>.
+
+Documentation
+--------------
+Documentation by Christian Couder <chriscool@tuxfamily.org> and the
+git-list <git@vger.kernel.org>, based on 'git tag' documentation.
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -536,6 +536,7 @@ LIB_OBJS += read-cache.o
 LIB_OBJS += reflog-walk.o
 LIB_OBJS += refs.o
 LIB_OBJS += remote.o
+LIB_OBJS += replace_object.o
 LIB_OBJS += rerere.o
 LIB_OBJS += revision.o
 LIB_OBJS += run-command.o
@@ -625,6 +626,7 @@ BUILTIN_OBJS += builtin-read-tree.o
 BUILTIN_OBJS += builtin-receive-pack.o
 BUILTIN_OBJS += builtin-reflog.o
 BUILTIN_OBJS += builtin-remote.o
+BUILTIN_OBJS += builtin-replace.o
 BUILTIN_OBJS += builtin-rerere.o
 BUILTIN_OBJS += builtin-reset.o
 BUILTIN_OBJS += builtin-rev-list.o

builtin-fsck.c

@@ -589,6 +589,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 	struct alternate_object_database *alt;
 
 	errors_found = 0;
+	read_replace_refs = 0;
 
 	argc = parse_options(argc, argv, prefix, fsck_opts, fsck_usage, 0);
 	if (write_lost_and_found) {

builtin-pack-objects.c

@@ -2098,6 +2098,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	int rp_ac_alloc = 64;
 	int rp_ac;
 
+	read_replace_refs = 0;
+
 	rp_av = xcalloc(rp_ac_alloc, sizeof(*rp_av));
 
 	rp_av[0] = "pack-objects";

builtin-prune.c

@@ -140,6 +140,7 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 	char *s;
 
 	save_commit_buffer = 0;
+	read_replace_refs = 0;
 	init_revisions(&revs, prefix);
 
 	argc = parse_options(argc, argv, prefix, options, prune_usage, 0);

builtin-replace.c

@@ -0,0 +1,159 @@
+/*
+ * Builtin "git replace"
+ *
+ * Copyright (c) 2008 Christian Couder <chriscool@tuxfamily.org>
+ *
+ * Based on builtin-tag.c by Kristian Høgsberg <krh@redhat.com>
+ * and Carlos Rica <jasampler@gmail.com> that was itself based on
+ * git-tag.sh and mktag.c by Linus Torvalds.
+ */
+
+#include "cache.h"
+#include "builtin.h"
+#include "refs.h"
+#include "parse-options.h"
+
+static const char * const git_replace_usage[] = {
+	"git replace [-f] <object> <replacement>",
+	"git replace -d <object>...",
+	"git replace -l [<pattern>]",
+	NULL
+};
+
+static int show_reference(const char *refname, const unsigned char *sha1,
+			  int flag, void *cb_data)
+{
+	const char *pattern = cb_data;
+
+	if (!fnmatch(pattern, refname, 0))
+		printf("%s\n", refname);
+
+	return 0;
+}
+
+static int list_replace_refs(const char *pattern)
+{
+	if (pattern == NULL)
+		pattern = "*";
+
+	for_each_replace_ref(show_reference, (void *) pattern);
+
+	return 0;
+}
+
+typedef int (*each_replace_name_fn)(const char *name, const char *ref,
+				    const unsigned char *sha1);
+
+static int for_each_replace_name(const char **argv, each_replace_name_fn fn)
+{
+	const char **p;
+	char ref[PATH_MAX];
+	int had_error = 0;
+	unsigned char sha1[20];
+
+	for (p = argv; *p; p++) {
+		if (snprintf(ref, sizeof(ref), "refs/replace/%s", *p)
+					>= sizeof(ref)) {
+			error("replace ref name too long: %.*s...", 50, *p);
+			had_error = 1;
+			continue;
+		}
+		if (!resolve_ref(ref, sha1, 1, NULL)) {
+			error("replace ref '%s' not found.", *p);
+			had_error = 1;
+			continue;
+		}
+		if (fn(*p, ref, sha1))
+			had_error = 1;
+	}
+	return had_error;
+}
+
+static int delete_replace_ref(const char *name, const char *ref,
+			      const unsigned char *sha1)
+{
+	if (delete_ref(ref, sha1, 0))
+		return 1;
+	printf("Deleted replace ref '%s'\n", name);
+	return 0;
+}
+
+static int replace_object(const char *object_ref, const char *replace_ref,
+			  int force)
+{
+	unsigned char object[20], prev[20], repl[20];
+	char ref[PATH_MAX];
+	struct ref_lock *lock;
+
+	if (get_sha1(object_ref, object))
+		die("Failed to resolve '%s' as a valid ref.", object_ref);
+	if (get_sha1(replace_ref, repl))
+		die("Failed to resolve '%s' as a valid ref.", replace_ref);
+
+	if (snprintf(ref, sizeof(ref),
+		     "refs/replace/%s",
+		     sha1_to_hex(object)) > sizeof(ref) - 1)
+		die("replace ref name too long: %.*s...", 50, ref);
+	if (check_ref_format(ref))
+		die("'%s' is not a valid ref name.", ref);
+
+	if (!resolve_ref(ref, prev, 1, NULL))
+		hashclr(prev);
+	else if (!force)
+		die("replace ref '%s' already exists", ref);
+
+	lock = lock_any_ref_for_update(ref, prev, 0);
+	if (!lock)
+		die("%s: cannot lock the ref", ref);
+	if (write_ref_sha1(lock, repl, NULL) < 0)
+		die("%s: cannot update the ref", ref);
+
+	return 0;
+}
+
+int cmd_replace(int argc, const char **argv, const char *prefix)
+{
+	int list = 0, delete = 0, force = 0;
+	struct option options[] = {
+		OPT_BOOLEAN('l', NULL, &list, "list replace refs"),
+		OPT_BOOLEAN('d', NULL, &delete, "delete replace refs"),
+		OPT_BOOLEAN('f', NULL, &force, "replace the ref if it exists"),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, options, git_replace_usage, 0);
+
+	if (list && delete)
+		usage_msg_opt("-l and -d cannot be used together",
+			      git_replace_usage, options);
+
+	if (force && (list || delete))
+		usage_msg_opt("-f cannot be used with -d or -l",
+			      git_replace_usage, options);
+
+	/* Delete refs */
+	if (delete) {
+		if (argc < 1)
+			usage_msg_opt("-d needs at least one argument",
+				      git_replace_usage, options);
+		return for_each_replace_name(argv, delete_replace_ref);
+	}
+
+	/* Replace object */
+	if (!list && argc) {
+		if (argc != 2)
+			usage_msg_opt("bad number of arguments",
+				      git_replace_usage, options);
+		return replace_object(argv[0], argv[1], force);
+	}
+
+	/* List refs, even if "list" is not set */
+	if (argc > 1)
+		usage_msg_opt("only one pattern can be given with -l",
+			      git_replace_usage, options);
+	if (force)
+		usage_msg_opt("-f needs some arguments",
+			      git_replace_usage, options);
+
+	return list_replace_refs(argv[0]);
+}

builtin-unpack-objects.c

@@ -495,6 +495,8 @@ int cmd_unpack_objects(int argc, const char **argv, const char *prefix)
 	int i;
 	unsigned char sha1[20];
 
+	read_replace_refs = 0;
+
 	git_config(git_default_config, NULL);
 
 	quiet = !isatty(2);

builtin.h

@@ -111,5 +111,6 @@ extern int cmd_write_tree(int argc, const char **argv, const char *prefix);
 extern int cmd_verify_pack(int argc, const char **argv, const char *prefix);
 extern int cmd_show_ref(int argc, const char **argv, const char *prefix);
 extern int cmd_pack_refs(int argc, const char **argv, const char *prefix);
+extern int cmd_replace(int argc, const char **argv, const char *prefix);
 
 #endif

cache.h

@@ -520,6 +520,7 @@ extern size_t packed_git_window_size;
 extern size_t packed_git_limit;
 extern size_t delta_base_cache_limit;
 extern int auto_crlf;
+extern int read_replace_refs;
 extern int fsync_object_files;
 extern int core_preload_index;
 
@@ -656,7 +657,11 @@ char *strip_path_suffix(const char *path, const char *suffix);
 
 /* Read and unpack a sha1 file into memory, write memory to a sha1 file */
 extern int sha1_object_info(const unsigned char *, unsigned long *);
-extern void * read_sha1_file(const unsigned char *sha1, enum object_type *type, unsigned long *size);
+extern void *read_sha1_file_repl(const unsigned char *sha1, enum object_type *type, unsigned long *size, const unsigned char **replacement);
+static inline void *read_sha1_file(const unsigned char *sha1, enum object_type *type, unsigned long *size)
+{
+	return read_sha1_file_repl(sha1, type, size, NULL);
+}
 extern int hash_sha1_file(const void *buf, unsigned long len, const char *type, unsigned char *sha1);
 extern int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned char *return_sha1);
 extern int pretend_sha1_file(void *, unsigned long, enum object_type, unsigned char *);

commit.h

@@ -123,6 +123,8 @@ struct commit_graft *read_graft_line(char *buf, int len);
 int register_commit_graft(struct commit_graft *, int);
 struct commit_graft *lookup_commit_graft(const unsigned char *sha1);
 
+const unsigned char *lookup_replace_object(const unsigned char *sha1);
+
 extern struct commit_list *get_merge_bases(struct commit *rev1, struct commit *rev2, int cleanup);
 extern struct commit_list *get_merge_bases_many(struct commit *one, int n, struct commit **twos, int cleanup);
 extern struct commit_list *get_octopus_merge_bases(struct commit_list *in);

environment.c

@@ -39,6 +39,7 @@ int pager_use_color = 1;
 const char *editor_program;
 const char *excludes_file;
 int auto_crlf = 0;	/* 1: both ways, -1: only when adding git objects */
+int read_replace_refs = 1;
 enum safe_crlf safe_crlf = SAFE_CRLF_WARN;
 unsigned whitespace_rule_cfg = WS_DEFAULT_RULE;
 enum branch_track git_branch_track = BRANCH_TRACK_REMOTE;

git.c

@@ -339,6 +339,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "receive-pack", cmd_receive_pack },
 		{ "reflog", cmd_reflog, RUN_SETUP },
 		{ "remote", cmd_remote, RUN_SETUP },
+		{ "replace", cmd_replace, RUN_SETUP },
 		{ "repo-config", cmd_config },
 		{ "rerere", cmd_rerere, RUN_SETUP },
 		{ "reset", cmd_reset, RUN_SETUP },

mktag.c

@@ -19,16 +19,17 @@
 /*
  * We refuse to tag something we can't verify. Just because.
  */
-static int verify_object(unsigned char *sha1, const char *expected_type)
+static int verify_object(const unsigned char *sha1, const char *expected_type)
 {
 	int ret = -1;
 	enum object_type type;
 	unsigned long size;
-	void *buffer = read_sha1_file(sha1, &type, &size);
+	const unsigned char *repl;
+	void *buffer = read_sha1_file_repl(sha1, &type, &size, &repl);
 
 	if (buffer) {
 		if (type == type_from_string(expected_type))
-			ret = check_sha1_signature(sha1, buffer, size, expected_type);
+			ret = check_sha1_signature(repl, buffer, size, expected_type);
 		free(buffer);
 	}
 	return ret;

object.c

@@ -188,17 +188,18 @@ struct object *parse_object(const unsigned char *sha1)
 	unsigned long size;
 	enum object_type type;
 	int eaten;
-	void *buffer = read_sha1_file(sha1, &type, &size);
+	const unsigned char *repl;
+	void *buffer = read_sha1_file_repl(sha1, &type, &size, &repl);
 
 	if (buffer) {
 		struct object *obj;
-		if (check_sha1_signature(sha1, buffer, size, typename(type)) < 0) {
+		if (check_sha1_signature(repl, buffer, size, typename(type)) < 0) {
 			free(buffer);
-			error("sha1 mismatch %s\n", sha1_to_hex(sha1));
+			error("sha1 mismatch %s\n", sha1_to_hex(repl));
 			return NULL;
 		}
 
-		obj = parse_object_buffer(sha1, type, size, buffer, &eaten);
+		obj = parse_object_buffer(repl, type, size, buffer, &eaten);
 		if (!eaten)
 			free(buffer);
 		return obj;